As a method of forming a high-quality semiconductor film, there is known an epitaxial growth technique of growing a single-crystal film on a substrate such as a wafer by the vapor phase growth. In a vapor phase growth apparatus that uses the epitaxial growth technique, a wafer is placed on a support portion inside a reaction chamber that is maintained in a normal pressure state or a reduced pressure state. Then, a process gas such as a source gas as a raw material for a film formation process is supplied from, for example, a shower plate of an upper portion of the reaction chamber to the surface of the wafer while heating the wafer. Thus, a thermal reaction of the source gas occurs on the surface of the wafer, and hence an epitaxial single-crystal film is formed on the surface of the wafer.
In recent years, a semiconductor device of GaN (gallium nitride) has been gaining attention as a material of a light emitting device or a power device. As the epitaxial growth technique that forms a GaN-based semiconductor, a metal organic chemical vapor deposition (MOCVD) is known. In the metal organic chemical vapor deposition, for example, organic metal such as trimethylgallium (TMG), trimethylindium (TMI), and trimethylaluminum (TMA) or ammonia (NH3) is used as the source gas. Also, there is a case in which hydrogen (H2) is used as a separation gas in order to suppress the reaction between the source gas.
In order to uniformly form a film on the surface of the wafer in the epitaxial growth technique, especially in MOCVD, it is important to appropriately mix the source gas, the separation gas, or the like and to supply the resultant gas to the surface of the wafer in a uniformly rectified state. JP 2001-81569 A discloses a configuration in which different gases are separated in different gas diffusion chambers until the source gas is introduced into the reaction chamber in order to appropriately mix the different gases.